1. Field of the Invention
The present invention relates to a piston-type compressor, in which fluid may be compressed by means of reciprocating pistons connected to a swash plate. More particularly, it relates to a guiding mechanism for reciprocating pistons, which improves control of the position of the pistons in the refrigerant compressor for an automotive air-conditioning system.
2. Description of the Prior Art
A swash plate refrigerant compressor with a variable displacement mechanism, particularly, a single head piston-type compressor suitable for use in an automotive air condition system, is disclosed in U.S. Pat. No. 4,664,604, which disclosure is incorporated herein by reference. Referring to FIGS. 1, 2, and 3, a cylinder block is accommodated in cylindrical housing 211 of a compressor. Pistons 48 are accommodated in cylinders 127 and are reciprocally movable therein. Drive shaft 115, which is driven by an engine, is rotatably supported by means of the central portion of the cylinder block and a front cover. Rotor plate 118 is mounted on drive shaft 115 and synchronously rotates with drive shaft 115. Further, swash plate 124 is tiltably mounted on drive shaft 115 and is reciprocally slidable together with spherical sleeve 129 parallel to the axis of drive shaft 115. Rotor plate 118 and swash plate 124 are connected to each other by means of a hinge mechanism. Swash plate 124 is engaged along its circumference with the interior portion of the associated piston(s) 48.
According to the above-described compressor, when drive shaft 115 is rotated, rotor plate 118 rotates together with drive shaft 115. The rotation of rotor plate 118 is transferred to swash plate 124 through the hinge mechanism. Rotor plate 118 is rotated with a surface inclined with respect to drive shaft 115, so that pistons 48 reciprocate in cylinder 127, respectively. Therefore, refrigerant gas is drawn into an inlet chamber and compressed and discharged from the inlet chamber into an associated discharge chamber, respectively.
Control of displacement of this compressor may be achieved by varying the stroke of piston 48. The stroke of piston 48 varies depending on the difference between pressures which are acting on the opposing sides of swash plate 124. This difference is created by variance between the pressure in a crank chamber acting on the rear surface 48a of piston 48 and suction pressure in cylinder 127 acting on the front surface 48b of piston 48, and acts on swash plate 124, through piston 48.
Cylinder housing 211 includes projection portion(s) 212 extending therefrom toward the interior of housing 211 and parallel to the reciprocating direction of piston(s) 48 for preventing the rotation of piston(s) 48 around its axis (their axes). In this arrangement, the frictional force between swash plate 124 and spherical sleeves 129 is generated because swash plate 124 slides in spherical sleeves 129 while rotating. Thereby, the frictional force acts on piston 48 to forcibly move them in the direction of the inner surface of cylinder 127 and urging them to rotate around the axis of piston 48.
Further, the inner surface of cylinder 127 functions to prevent piston 48 from inclining in a radial direction except for its rotation. However, it is difficult for cylinder 127 to prevent piston 48 from inclining in a radial direction when piston 48 approaches a bottom dead center position because the area of contact between piston 48 and cylinder 127 relative to the length of the piston within the cylinder decreases in comparison with that of existing near a top dead center position of piston 48, though cylinder 127 may prevent piston 48 from inclining in a radial direction when piston 48 approaches a top dead center position.
Therefore, in existing designs, pistons 48 experience rapid wear on their peripheral surfaces. As a result, compressor durability is reduced and noise and vibration of the compressor increase.